Power Conversion and Control Systems and Methods for Solid-State Lighting

ABSTRACT

A solid-state lighting system comprises a plurality of light-emitting devices (e.g., light-emitting diodes) and an alternating current to direct current (AC-DC) converter that converts AC power to DC power for powering the plurality of light-emitting devices. The AC-DC converter is configured to perform AC-DC conversion directly, without the need for or use of a bridge rectifier or step-down transformer. According to one aspect of the invention, the light-emitting devices of the solid-state lighting system are autonomous and individually powered by a plurality of DC power supplies generated from the DC power produced by the AC-DC converter. According to another aspect, a plurality of phase-offset dimmer control signals are generated based on waveform distortions in a dimming signal produced by a conventional dimmer switch. The phase-offset dimmer control signals are used to individually control the dimming of the light-emitting devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/897,066 filed on Oct. 4, 2010, the disclosure of which isincorporated herein by reference, in its entirety and for all purposes.

FIELD OF THE INVENTION

The present invention relates in general to electrical power conversionand control methods and systems, and in particular to electrical powerconversion and control methods and systems for solid-state lighting,such as, for example, light-emitting diode (LED) lighting.

BACKGROUND OF THE INVENTION

Due to their high efficiency and durability, light-emitting diodes(LEDs) are desirable candidates for providing general lighting in homes,offices and other environments. Whereas conventional incandescent lampsare only about 3% efficient, LEDs have efficiencies of 30% or higher.LED lifetimes are also over 20 times longer than incandescent lamps andover 5 times longer than compact fluorescent lamps.

Although the lighting performance characteristics of LEDs are superiorto more conventional lighting technologies, widespread adoption of LEDlighting has been slow. The primary reason for the delay is that LEDbulbs are expensive. In fact, at the present time LED bulbs cost about10-25 times more than incandescent bulbs of comparable light output.

The high price of LED bulbs is significantly impacted by the costsinvolved in their manufacture, in particular the costs involved inmanufacturing the power conversion circuitry needed to power the LEDbulbs. Incandescent bulbs receive power directly from the AC mains.However, LED bulbs are DC powered. Consequently, if power from the ACmains is to be used, an LED bulb must be equipped with power conversioncircuitry to convert the AC mains power to DC power.

FIG. 1 is a drawing of a prior art LED bulb 100, illustrating how ACpower from the AC mains is converted to DC in existing LED bulbs. First,a bridge rectifier (i.e., diode bridge) 102 rectifies the AC inputvoltage Vin from the AC mains to DC. The rectified voltage is thenfiltered by a smoothing circuit, which in its simplest form comprises asmoothing capacitor 104 coupled to the output of the bridge rectifier102. Finally, a DC-DC converter 106 steps down the rectified andfiltered voltage to the appropriate DC output voltage Vout needed topower the LEDs in an LED string 108. The DC output voltage Vout is setbased on the number of LEDs that are in the LED string 108, the numberwhich is determined during design depending on required light outputlevel (i.e., lumens) of the LED light bulb 100. Physically, the LEDs ofthe LED string 108 are arranged in a cluster and encased by diffuserlenses, which spread the light produced by the LEDs.

One well-known problem with the power conversion circuitry of the LEDbulb 100 is that the bridge rectifier 102 and smoothing capacitor 104present a nonlinear load to the AC mains. This nonlinearity causes theinput current Iin from the AC mains to be drawn in the form of a seriesof narrow current pulses, as illustrated in FIG. 2. The narrow currentpulses are rich in harmonics of the line frequency and characteristic ofa power converter having a low power factor. Power factor is adimensionless number between 0 and 1, describing how effectively a powerconverter is at transferring real power from an AC power source to aload. A low power factor is highly undesirable since it results inreduced conversion efficiency, heating in the AC mains generator anddistribution systems, and noise that can interfere with the performanceof other equipment.

To avoid problems associated with a low power factor, practical AC-DCpower converters typically employ a power factor correction (PFC)pre-regulator 302 between the output of the bridge rectifier 102 and theinput of the DC-DC converter 106, as illustrated in FIG. 3. The PFCpre-regulator 302 functions to force the input current Iin to be moresinusoidal and in phase with the AC input voltage Vin, therebyincreasing the power factor. Unfortunately, introduction of the PFCpre-regulator 302 lowers energy efficiency, increases parts count andmanufacturing costs, and makes it difficult to package the LED bulb 300in a small form factor. Moreover, the PFC pre-regulator 302 usuallycontains a boost converter that generates high voltages. These highvoltages tend to stress the LED bulb's 300 parts, leading to reliabilityproblems. The high voltages also pose safety concerns.

Yet another problem with existing LED bulbs relates to their inherentinability to be controlled by conventional dimmer switches. Many homesand offices have dimmer switches that were designed to control thedimming of incandescent bulbs. It would be desirable to be able to usethose pre-installed dimmer switches to control the dimming of LED bulbs.

FIG. 4 is a circuit diagram showing a conventional dimmer switch 400.The dimmer switch 400 comprises a variable resistor 402, a capacitor404, a DIAC (diode for alternating current) 406, and a TRIAC (triode foralternating current) 408. The TRIAC 408 is triggered when the voltageacross the capacitor 404 exceeds the breakdown voltage of the DIAC 406.The voltage increases and decreases according to the cycling of the ACinput voltage Vin, and triggering of the TRIAC 408 is delayed for eachpositive and negative half cycle depending on the RC delay presented bythe variable resistor 402 and capacitor 404. Accordingly, the turn-ondelay 512 results in a distorted dimming waveform with a lower averagepower, as illustrated in FIG. 5B. In angular terms, the turn on delay512 is referred to in the art as the “firing angle” (180°−θ), where θ isknown as the “conduction angle.” The ability to control the firing angleby adjusting the variable resistor 402 therefore provides the ability tocontrol the average power delivered to the incandescent bulb 410 and,consequently, the dimming of the incandescent bulb 410.

The TRIAC dimmer switch 400 is suitable for controlling the dimming ofincandescent bulbs. Unfortunately, it does not provide an acceptablesolution for dimming existing LED bulbs, like the prior art LED bulbs100 and 300 in FIGS. 1 and 3. Incandescent bulbs present a resistiveload during all portions of the AC input waveform cycle. However, LEDsare nonlinear devices and draw significantly less current than doincandescent bulbs. At increased dimming (i.e., low light output levels)in particular, the current drawn by the LEDs of existing LED bulbs canbe so small that the current drops below the holding current of theTRIAC 408. Under these conditions, the TRIAC 408 can retrigger or turnOFF, resulting in annoying LED flickering, or the LED bulb prematurelyturning OFF before reaching the desired dimming level. The presence ofthe AC-DC power conversion circuitry between the AC power source andLEDs can also interfere with the ability of the TRIAC dimmer switch 400to control the dimming of the LEDs.

Considering the foregoing drawbacks and limitations of existing LEDbulbs, it would be desirable to have power conversion and controlmethods and apparatus for LED bulbs that are energy-efficient,inexpensive to manufacture, compact, safe to use, reliable, and providethe ability to control the dimming of LEDs of the LED bulb over a widedimming range using conventional dimmer switches.

SUMMARY OF THE INVENTION

Solid-state lighting systems and power conversion and control methodstherefor are disclosed. An exemplary solid-state lighting systemcomprises a plurality of light-emitting devices (e.g., light-emittingdiodes) and an alternating current to direct current (AC-DC) converterthat converts AC power to DC power for powering the plurality oflight-emitting devices. The AC-DC converter is configured to performAC-DC conversion directly, without the need for or use of a bridgerectifier or step-down transformer. According to one aspect of theinvention, the light-emitting devices of the solid-state lighting systemare autonomous and individually powered by a plurality of DC powersupplies generated from the DC power produced by the AC-DC converter.According to another aspect, a plurality of phase-offset dimmer controlsignals are generated based on waveform distortions in a dimming signalproduced by a conventional dimmer switch. The phase-offset dimmercontrol signals are used to control the dimming of the plurality oflight-emitting devices.

The solid-state lighting systems and methods of the present inventionoffer a number of advantages over prior art solid-state lighting systemsand methods. First, the solid-state lighting systems of the presentinvention have a lower parts count and are less costly to manufacturethan prior art solid-state lighting systems. Using the disclosed AC-DCconverter obviates the need for bridge rectifiers, step-downtransformers, and power factor correction pre-regulator circuitry, andmost, if not all of the solid-state lighting system components areamenable to being formed in one or more integrated circuit (IC) chips.The reduced parts count and ability to form the solid-state lightingsystem components in one or more IC chips lowers manufacturing costs andaffords the ability to realize economies of scale. Second, the AC-DCconverter, reduced parts count, and ability to form some or all of thepower conversion and control components in one or more IC chips, allcontribute to the ability to manufacture a solid-state lighting systemthat is more energy efficient than prior art solid-state lightingsystems. Third, the solid-state lighting systems of the presentinvention are more reliable and have a longer lifetime than prior artsolid-state lighting systems. Powering the light-emitting devices of thesolid-state lighting system of the present invention using separatepower supplies results in increased reliability, and configuring thelight-emitting devices so that they are autonomous and individuallydimmable allows the solid-state lighting system of the present inventionto last longer, since the entire system will not completely fail if justone or a couple of the light-emitting devices fail. Finally, thesolid-state lighting systems of the present invention provide the highlydesirable benefit of being dimmable in response to conventional dimmerswitches, even to very low light levels and without flickering orpremature light cut-off.

Further features and advantages of the invention, including descriptionsof the structure and operation of the above-summarized and otherexemplary embodiments of the invention, will now be described in detailwith respect to accompanying drawings, in which like reference numbersare used to indicate substantially identical or functionally similarelements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing of a prior art LED bulb;

FIG. 2 is a signal diagram of the input line voltage Vin applied to andinput line current Iin drawn from the AC mains for the prior art LED inFIG. 1;

FIG. 3 is drawing of a prior art LED bulb equipped with a power factorcorrection (PFC) pre-regulator;

FIG. 4 is circuit diagram of a conventional phase control (i.e., TRIAC(triode for alternating current)) dimmer switch;

FIGS. 5A and 5B are line voltage Vin and dimming waveforms associatedwith the TRIAC dimmer switch in FIG. 4;

FIG. 6 is a drawing of an LED bulb, according to an embodiment of thepresent invention;

FIG. 7 is a drawing of the LED bulb in FIG. 6, illustrating how the LEDsof the LED bulb are enclosed in a transparent or translucent enclosureand how the electrical components of the LED bulb are coupled to astandard Edison screw base;

FIG. 8 is a circuit diagram of an alternating current to direct current(AC-DC) converter that used to implement the AC-DC converter of the LEDbulb in FIG. 6;

FIG. 9 is a signal diagram of the AC input voltage Vin supplied to theAC-DC converter in FIG. 8, and its relationship to the DC voltage Vdcproduced at the output of the AC-DC converter and its inverse −Vdc;

FIG. 10 is a table showing how the switches of the AC-DC converter inFIG. 8 are switched and driven, depending on the instantaneous value ofthe AC input voltage Vin compared to the DC voltage Vdc produced at theoutput of the AC-DC converter in FIG. 8 and its inverse −Vdc;

FIG. 11A is a circuit diagram illustrating how the AC-DC converter inFIG. 8 reduces to and operates as a buck converter during times ofpositive half cycles of the AC input waveform when Vin>Vdc;

FIG. 11B is a circuit diagram illustrating how the AC-DC converter inFIG. 8 reduces to and operates as an inverting buck converter duringtimes of negative half cycles of the AC input waveform when Vin<−Vdc;

FIG. 12 is a circuit diagram of a charge pump divider that may be usedto implement the divider in the LED bulb in FIG. 6;

FIG. 13A is a simplified equivalent circuit diagram of the charge pumpdivider in FIG. 12 when the charge pump divider is configured in a“charge” state;

FIG. 13B is a simplified equivalent circuit diagram of the charge pumpdivider in FIG. 12 when the charge pump divider is configured in a“load” state;

FIG. 14 is a drawing illustrating how the dimming of the LEDs of the LEDbulb in FIG. 6 may be controlled by a conventional TRIAC dimmer switch;

FIGS. 15A-D are signal diagrams associated with the operation of the LEDbulb in FIG. 6 when the TRIAC dimmer switch in FIG. 14 is not active;

FIGS. 16A-D are signal diagrams associated with the operation of the LEDbulb in FIG. 6 when the TRIAC dimmer switch in FIG. 14 is active;

FIG. 17 is a comparison circuit that compares the dimmer waveform of theTRIAC dimmer switch in FIG. 14 to the DC voltage at the output of theAC-DC converter;

FIG. 18 is a circuit diagram of a frequency translator that may be usedto transform duty cycle information in the logic signal S from thecomparison circuit in FIG. 17 to a higher frequency;

FIGS. 19A and 19B are signal diagrams illustrating how the DIM signalproduced by the frequency translator in FIG. 18 has a high duty cyclefor minimum dimming (FIG. 19A) and a low duty cycle for maximum dimming(FIG. 19B);

FIG. 20 is a circuit diagram of a phase generator that may be used togenerate a plurality of dim control signals of different phases forcontrolling the dimming of the plurality of LEDs of the LED bulb in FIG.6;

FIG. 21 is a circuit diagram of one of the synchronous phase-frequencydetectors (S-PFDs) used in the phase generator in FIG. 20; and

FIG. 22 is a drawing of an LED bulb, according to an alternativeembodiment of the present invention, in which the LEDs of the LED bulbare connected in parallel.

DETAILED DESCRIPTION

The exemplary embodiments of the present invention set forth below aredescribed and illustrated in the context of solid-state lighting,particularly power conversion and control methods and systems for LEDlighting. It is to be emphasized and understood, however, that the powerconversion and control methods of the present invention are not limitedto LED lighting applications; they are applicable to other lighting andnon-lighting applications employing other types of loads, includingsolid-state (or non-solid-state) lighting devices other than LEDs, anddevices that do not emit light but perform some other useful function.

Referring to FIG. 6, there is shown a light-emitting diode (LED) bulb600, according to an embodiment of the present invention. The LED bulb600 comprises power conversion and control circuitry 601 that includesan alternating current to direct current (AC-DC) converter 602, adivider 604, and an LED controller 606; and LEDs 608-1, 608-2, . . . ,608-n, where n is an integer indicating that the LEDs may comprise oneor a plurality of LEDs. As will be explained in detail below, the AC-DCconverter 602 directly converts AC power, such as may be provided by theAC mains, to DC power. The divider 604 divides the DC voltage Vdc of theDC power generated by the AC-DC converter 602 by a factor m, therebygenerating one or a plurality m of separate power supplies for poweringthe n LEDs 608-1, 608-2, . . . , 608-n. The factor m is an integer, andin one embodiment is an integer having the same value as n. The LEDcontroller 606 comprises one or more controlled current sources forcontrolling the currents passing through the LEDs 608-1, 608-2, . . . ,608-n and, optionally, further includes circuitry that affords theability to control the dimming of the LEDs 608-1, 608-2, . . . , 608-nusing a conventional dimmer switch.

In one embodiment of the invention, some or all of the variouscomponents of the power conversion and control circuitry 601 comprise asingle integrated circuit (IC) chip. In another embodiment, some or allof the various components of the power conversion and control circuitry601 comprise and are distributed among two or more IC chips. However,any number and combination of IC chips, hybrid circuits, or discretedevices may be used to implement the power conversion and controlcircuitry 601 of the LED bulb 600, as will be readily appreciated andunderstood by those of ordinary skill in the art.

The LEDs 608-1, 608-2, . . . , 608-n of the LED bulb 600 are configuredwithin a transparent or translucent enclosure, and the AC-DC converter602, divider 604, and LED controller 606 are integrated in or attachedto a base that is compatible with a standardized receptacle or socket.For example, in one embodiment, the transparent or translucent enclosurecomprises a glass bulb 702, and the AC-DC converter 602, divider 604,and LED controller 606 are attached to or integrated within an Edisonscrew base 704, as illustrated in FIG. 7. Other types of transparent ortranslucent enclosures (standardized or non-standardized) and other basetypes (standardized or non-standardized) may be used, as will beappreciated by those of ordinary skill in the art. Accordingly, for thepurpose of this disclosure the term “LED bulb” refers to and encompasseswithin its meaning an LED lighting apparatus having any type ofenclosure and any type of base.

FIG. 8 is a circuit diagram of an AC-DC converter 800 used to implementthe AC-DC converter 602 of the LED bulb 600 in FIG. 6, according to oneembodiment of the present invention. The AC-DC converter 800 is similarto the AC-DC converter disclosed in co-pending and commonly owned U.S.patent application Ser. No. 12/841,608, entitled AC/DC Power ConversionMethods and Apparatus, which is hereby incorporated into this disclosureby reference.

As shown in FIG. 8, the AC-DC converter 800 comprises first, second,third and fourth switches 802, 804, 806 and 808, an inductor 810, asmoothing capacitor 812, and a switch control 814. The first switch 802is coupled between one terminal of the AC input and a first terminal ofthe inductor 810; the second switch 804 is coupled between the firstterminal of the inductor 810 and the opposing-polarity terminal of theAC input; the third switch 806 is coupled between the AC input and thesecond terminal of the inductor 810; and the fourth switch 808 iscoupled between the second terminal of the inductor 810 and the positiveDC output terminal. The switch control 814 generates switch drivesignals for controlling the switching of the first, second, third andfourth switches 802, 804, 806 and 808, depending on the instantaneous ACinput voltage Vin compared to the DC output voltage, as is explained inmore detail below.

In one embodiment of the invention, the first, second, third, and fourthswitches 802, 804, 806 and 808 comprise silicon-based transistors (e.g.,metal-oxide-semiconductor field-effect transistors (MOSFETs) or bipolarjunction transistors (BJTs)) of an integrated circuit (IC) chipmanufactured according to a standard semiconductor manufacturingprocess. The inductor 810 and capacitor 812 may also be integrated inthe one or more IC chips, or either or both of these devices may bediscrete devices coupled to external pins of the one or more IC chips.Of course, other types of switching devices and semiconductormanufacturing processes may be used. For example, conventional switches,diodes, relays, or other semiconductor-based or non-semiconductor-basedswitching device may be used, or compound-semiconductor-based transistordevices, such as high electron mobility transistors (HEMTs) orheterojunction bipolar transistors (HBTs), may be used to implement thefirst, second, third, and fourth switches 802, 804, 806 and 808switches, instead of silicon-based MOSFETs or BJTs. For the purpose ofthis disclosure, the term “switch” is used in its broadest sense toinclude all of these types of switches and any other suitable switchingdevice.

The AC-DC converter 800 operates by converting an AC input voltage Vin,such as may be provided by the AC mains, to a DC output voltage Vdc,without the need for a bridge rectifier (i.e., diode bridge). DirectAC-DC conversion is accomplished by controlling the ON-OFF states of thefirst, second, third, and fourth switches 802, 804, 806 and 808 usingthe switch control 814. The switches 802, 804, 806 and 808 are turned ON(closed), turned OFF (opened), driven by a switch drive signal of dutycycle D, or driven by a complementary switch drive signal of duty cycle(1−D), depending on the instantaneous AC input voltage Vin compared tothe DC output voltage Vdc. The switch drive signal and the complementaryswitch drive signal are generated by the switch control 814 and in oneembodiment have a common, fixed switching (i.e., “chopping”) frequencyf=1/T, where T is the switching period. To avoid the need for physicallylarge and expensive capacitors, the chopping frequency f of the switchcontrol is set at a high frequency of about 1 MHz or higher.

As illustrated in the signal diagram in FIG. 9 and shown in theswitching table in FIG. 10, when Vin>Vdc, the first switch 802 is drivenby the switch drive signal at a duty cycle t_(ON)/T=D, the second switch804 is driven by the complementary switch drive signal at a duty cycle(T−t_(ON))/T=(1−D), the third switch 806 is turned OFF, and the fourthswitch 808 is turned ON. When Vin<−Vdc, the first switch 802 is turnedOFF, the second switch 804 is turned ON, the third switch 806 is drivenby the switch drive signal at a duty cycle D, and the fourth switch isdriven by the complementary switch drive signal at a duty cycle (1−D).Finally, when Vin is greater than −Vdc but less than Vdc, i.e. when|Vin|<Vdc, the first, second, third, and fourth switches 802, 804, 806and 808 are all turned OFF.

The AC-DC converter 800 produces a DC output voltage Vdc=D|Vin|, as canbe understood by observing that the AC-DC converter 800 actuallycomprises an integrated (i.e., conjoined) buck converter and invertingbuck converter. During positive half cycles of the AC input waveformwhen Vin>Vdc, the third switch 806 is OFF, the fourth switch 808 is ON,and the AC-DC converter 800 reduces to and operates as a buck converter800A, as illustrated in FIG. 11A. In this configuration the first andsecond switches 802 and 804 serve as the high-side and low-side switchesof the buck converter and are driven by the switch drive signal at dutycycle D and complementary switch drive signal at a duty cycle (1−D),respectively. The first and second switches 802 and 804 thereforealternately configure the inductor 810 between storing energy andsupplying current during positive half cycles of the AC input voltagewhen Vin>Vdc, and the DC output voltage Vdc=DVin.

During negative half cycles of the AC input waveform when Vin<−Vdc, thefirst switch 802 is OFF, the second switch 804 is ON, and the AC-DCconverter 800 reduces to and operates as what may be referred to as an“inverting” buck converter 800B, as illustrated in FIG. 11B. In thisconfiguration the third and fourth switches 806 and 808 are driven bythe switch drive signal D and complementary switch drive signal (1−D),respectively. The inverting buck converter 800B inverts the negativeinput voltage Vin, alternately configuring the inductor 810, by theswitching action of the third and fourth switches 806 and 808, betweenstoring energy and supplying current during the negative half cycles ofthe AC input voltage when Vin<−Vdc, to produce an output voltage Vdcequal to D|Vin|. Hence, considering both positive and negative halfcycles, the AC-DC converter 800 produces a DC output voltage Vdc=D|Vin|.

In the exemplary embodiment described above, the switch control circuit814 controls the opening and closing of the switches 802, 804, 806 and808 according to the switching table in FIG. 10 for all load conditions.In another embodiment, the switch control 814 is configured to holdswitch 808 open during light load conditions, and the remaining switches802, 804 and 806 are configured to operate according to the switchingtable in FIG. 10 (or are configured to not switch at all). Accordingly,in this alternative embodiment, the capacitor 812 serves as the DC powersupply source during light load conditions.

One important advantage of using the AC-DC converter 800 is that itperforms AC-DC conversion directly, without the need for or use of abridge rectifier or step-down transformer. This obviates the need forpower factor correction pre-regulator circuitry to compensate for thenonlinearity presented by the bridge rectifier. This advantage resultsin an LED bulb 600 that has a lower parts count, that is less expensiveto manufacture, and which is capable of being designed to have a muchsmaller physical size (i.e., smaller form factor) than prior art LEDbulbs. It also results in an LED bulb 600 that is more energy efficient,more reliable, and safer to use.

According to an embodiment of the invention, each of the LEDs of the LEDbulbs of the present invention is autonomous and individually powered bya separate power supply. In the exemplary embodiment shown in FIG. 6,this aspect of the invention is realized by configuring the divider 604to generate and provide a plurality m of separate power supplies ofvoltage Vdc/m for powering the n LEDs 608-1, 608-2, . . . , 608-n of theLED bulb 600. Having autonomous and independently-powered LEDs 608-1,608-2, . . . , 608-n allows for graceful degradation of the LED bulb600, since if one of the LEDs fails 608-1, 608-2, . . . , 608-n theothers can remain lit.

FIG. 12 is a circuit diagram of a charge pump divider 1200 that can beused to generate the m power supplies provided by the divider 604. Forthe purpose of this illustration, it is assumed that the LED bulb 600contains four LEDs (i.e., n=4), and that four charge pump dividers 1200are correspondingly employed to generate m=n=4 separate power supplies,each power supply having a voltage Vdc/4. Those of ordinary skill in theart will understand, of course, that this is only an example and thatthe LED bulb 600 is not limited to having four LEDs, and that the chargepump divider 1200 can be modified to generate other numbers m of powersupplies.

As shown in FIG. 12, the charge pump divider 1200 comprises a first setof switches 1202-1, 1202-2, 1202-3, 1202-4; capacitors 1204-1, 1204-2,1204-3, 1204-4; second set of switches 1206-1, 1206-2, 1206-3, 1206-4;and an oscillator 1208. The charge pump divider 1200 is configured tosupply power to LED 608-1, which is driven by a controlled currentsource 1210 that is enabled and disabled according to a dimmer signalDIM, as will be discussed in more detail below. Substantially identicalcharge pump dividers are employed to generate and supply power to theremaining LEDs 608-2, . . . , 608-n. The first set of switches 1202-1,1202-2, 1202-3, 1202-4 and second set of switches are 1206-1, 1206-2,1206-3, 1206-4 alternately configure the capacitors 1204-1, 1204-2,1204-3, 1204-4 in a “charge” state and a “load” state, in response toperiodic switch (i.e., charge state) control signals CS and CS providedby the oscillator 1208. When in the charge state, the switches of thefirst set of switches 1202-1, 1202-2, 1202-3, 1202-4 are all closed andthe switches of the second set of switches are all open, resulting inthe capacitors 1204-1, 1204-2, 1204-3, 1204-4 being coupled in series,as illustrated in the charge-state equivalent circuit in FIG. 13A. Thecapacitors 1204-1, 1204-2, 1204-3, 1204-4 all have the same capacitance.Consequently, the DC voltage Vdc is divided and distributed evenly(Vdc/4) among the series-connected capacitors 1204-1, 1204-2, 1204-3,1204-4. After the capacitors 1204-1, 1204-2, 1204-3, 1204-4 havecharged, the switch control signals CS and CS cause the first set ofswitches 1202-1, 1202-2, 1202-3, 1202-4 to open and the second set ofswitches 1206-1, 1206-2, 1206-3, 1206-4 to close, configuring the chargepump divider 1200 in the load state, as illustrated in the load-stateequivalent circuit in FIG. 13B. In the load state, the charged,parallel-connected capacitors 1204-1, 1204-2, 1204-3, 1204-4collectively supply power to the LED 608-1.

According to one embodiment of the invention illustrated in FIG. 14, theLED bulb 600 of the present invention is dimmable using a conventionalTRIAC (triode for alternating current) dimmer switch 1402. The TRIACdimmer switch 1402 is shown by a dashed box to emphasize that in thisexemplary embodiment it is separate from the LED bulb 600. However, inanother embodiment it (or other similar dimmer switch) comprises part ofthe LED bulb 600.

As was explained above in reference to FIGS. 4 and 5 above, a TRIACdimmer distorts the AC input waveform so that the average powerdelivered to the bulb is reduced. By itself the TRIAC dimmer switch doesnot provide an acceptable solution for controlling the dimming of theLED bulbs of the present invention. However, the distorted voltagewaveform (i.e., modified input voltage Vin′) that it produces doescontain information that can be used to control the dimming. Asillustrated in FIG. 15A, with no dimming active, the modified inputvoltage Vin′ provided by the TRIAC dimmer switch 1402 is substantiallythe same as the AC input voltage Vin supplied by the AC mains. Underthis condition, FIGS. 15B and 15C show that Vin′ is greater than Vdc orless than −Vdc for appreciable portions of the AC cycle period, and FIG.15D shows that |Vin′| is less than Vdc for only very short periods oftime t1. However, when dimming is active and waveform distortion isapplied by the TRIAC dimmer switch 1402 (see FIG. 16A), the modifiedinput voltage Vin′ remains greater than Vdc or less than −Vdc forshorter portions of the AC cycle period (see FIGS. 16B and 16C) and|Vin′| remains less than Vdc for longer durations of time t2, i.e.,t2>t1 (see FIG. 16D).

To exploit this pulse-width versus dimming-level dependency incontrolling the dimming of the LEDs 608-1, 608-2, . . . , 608-n of theLED bulb 600, the LED controller 606 of the LED bulb 600 includes acomparison circuit 1700, shown in FIG. 17, which operates to generate alogic signal S indicative of times when |Vin′|<Vdc. The comparisoncircuit 1700 comprises first and second comparators 1702 and 1704, aninverting amplifier 1706, a first voltage divider including resistors1708 and 1710 (or, alternatively, capacitors), a second voltage dividerincluding resistors 1712 and 1714 (or, alternatively, capacitors), and alogic NOR gate 1716. The first and second voltage dividers may not benecessary depending on the acceptable input voltage ranges of thevarious amplifiers. If, however, the modified AC input voltage Vin′ isnot within the acceptable input ranges, it is scaled down using thefirst and second voltage dividers. Specifically, the first voltagedivider scales the modified input voltage Vin′ down to a scaled,modified AC input voltage αVin′ so that the voltage is within theacceptable input voltage range limit of the first and second comparators1702 and 1704, and the second voltage divider scales the DC outputvoltage Vdc of the AC-DC converter 602 by the same amount to produce ascaled DC output voltage αVdc. The first comparator 1702 compares thescaled, modified AC input voltage αVin′ to the scaled DC output voltageαVdc, producing a high output voltage when Vin′>Vdc and a low outputvoltage when Vin′<Vdc. The inverting amplifier 1706 inverts the scaledDC output voltage αVdc to produce a scaled, inverted DC output voltage−αVdc. The second comparator 1704 compares the scaled, inverted DCoutput voltage −αVdc to the scaled, modified AC input voltage a Vin′,producing a high output voltage when Vin′<−Vdc and a low output voltagewhen Vin′>−Vdc. Finally, the NOR gate generates the desired logic signalS, which has a logic high (“1”) whenever |Vin′|<Vdc and a logic low(“0”) for all other times.

The logic signal S has a variable duty cycle that depends on the dimsetting of the TRIAC dimmer switch 1402. In accordance with anembodiment of the present invention, this dependency is used to controlthe dimming of the LEDs 608-1, 608-2, . . . , 608-n of the LED bulb 600,specifically by duty cycling the ON-OFF ratio of the LEDs 608-1, 608-2,. . . , 608-n. Because the logic signal S has a low frequency equal toonly that of the line frequency (60 Hz in the United States), however,it is first translated up in frequency in order to avoid anyperceptibility of LED flickering, as will be explained in detail below.While the logic signal S in this exemplary embodiment is generated basedon times when the comparison circuit 1700 determines that |Vin′|<Vdc, itshould be pointed out that the logic signal S may be alternativelygenerated based on other signal characteristics in the distortedwaveform Vin′, such as, for example, the firing angle or conductionangle of the distorted waveform Vin′.

FIG. 18 is a circuit diagram of an exemplary frequency translator 1800used to transform the duty cycle information in the logic signal S to ahigher frequency. In one embodiment, it is included within the LEDcontroller 606 of the LED bulb 600 and comprises first and seconddigital counters 1802 and 1804, a latch 1806, and a digital magnitudecomparator 1808. The logic signal S from the comparison circuit 1700 iscoupled to the enable (EN) input of the first digital counter 1802,which begins counting from zero at a rate of 2⁷×60 Hz when the logicsignal is a logic high, i.e., when |Vin′|<Vdc. The first digital counter1802 counts until the logic signal S drops to a logic low, at which timethe digital count is latched into the latch 1806 and coupled to input Bof the digital magnitude comparator 1808. The second digital counter1804 is a free-running counter that is configured to continuously andrepeatedly count from 0 to 127, but at a rate much higher than the 60 Hzline rate, allowing the duty cycle information in the logic signal S tobe translated to a higher frequency f_(LED). f_(LED) is set duringdesign and in one embodiment is equal to 10 MHz. As the second digitalcounter 1804 counts, the digital comparator 1808 compares its count tothe count held by the latch 1806. Eventually, the count exceeds thecount held by the latch 1806, causing the A>B output of the digitalcomparator 1808 to change to a logic high. The A>B output remains at alogic high until the second digital counter 1804 counts to its limit(2⁷−1=127). It then drops low and the second digital counter 1804 resetsto zero to begin counting anew.

The A>B output signal of the digital comparator 1808 has a fixed highfrequency f_(LED) and a variable duty cycle dependent upon the dim levelsetting of the TRIAC dimmer switch 1402. For a minimum dim setting theduty cycle (t_(ON)/t_(OFF)) of the A>B signal is high, as illustrated inFIG. 19A, and for a maximum dim setting the duty cycle is low, asillustrated in FIG. 19B. The A>B signal can therefore be used to controlthe dimming of the LED bulb 600 over a wide dimming range by simply dutycycling the ON-OFF ratios of the LEDs 608-1, 608-2, . . . , 608-n.According to one embodiment, the A>B signal is used as the “DIM” signalfor enabling and disabling one or more controlled current sources thatdrive the LEDs 608-1, 608-2, . . . , 608-n, similar to as shown in FIG.12, where the controlled current source 1210 of the LED 608-1 is enabledand disabled in response to the DIM signal and in accordance with theDIM signal's duty cycle.

Depending on the number of LEDs being used in the LED bulb 600,simultaneous switching of the LEDs 608-1, 608-2, . . . , 608-n ON andOFF by the same DIM signal may result in excessive loading. To avoidthis problem, in one embodiment of the invention n dim control signalsφ₁, φ₂, . . . , φ_(n), each of a different phase with respect to theother, are generated and used to individually control the duty cyclingof the ON-OFF ratio of the n LEDs 608-1, 608-2, . . . , 608-n. FIG. 20is a circuit diagram of an exemplary phase generator 2000 that may beused to generate the n dim control signal φ₁, φ₂, . . . , φ_(n). In oneembodiment of the invention, the phase generator 2000 comprises part ofthe LED controller 606 of the LED bulb 600 and includes master and slavering oscillators 2002 and 2004 (or other type of multi-phaseoscillators) and n synchronous phase-frequency detectors (S-PFDs)2006-1, 2006-2, . . . , 2006-n. A more detailed circuit diagram of thefirst S-PFD 2006-1 is shown in FIG. 21, the remaining S-PFDs 2006-2, . .. , 2006-n being substantially the same.

The master ring oscillator 2002 is configured in a phase-locked loop2008, which operates to lock the output frequency of the master ringoscillator 2002 to f_(LED) and provide master phase references forcomparison to the phases of the slave ring oscillator 2004. The A>Bsignal from the digital magnitude comparator 1808 of the frequencytranslator 1800 (FIG. 18) is used as a phase rotation command forshifting the phases of the slave ring oscillator 2004 relative to thephases of the master ring oscillator 2002. The S-PFDs 2006-1, 2006-2, .. . , 2006-n generate the n dim control signals φ₁, φ₂, . . . , φ_(n)each of which has pulse of widths proportional to the phase differenceof the phases of the master and slave ring oscillators 2002. An XOR gate2010 compares the pulse widths of one of the S-PFDs (in this exampleS-PFD 2006-1) to the pulse widths in the A>B signal. When the comparedpulse widths fail to match, the XOR gate 2010 generates a perturbationpulse. Over time these perturbation pulses are averaged by the filter2012, to produce a perturbation signal that is used to alter the powersupply of the slave oscillator 2004. Modifying the slave oscillatorpower supply affects the delays of the inverters in the slave ringoscillator 2004 and, consequently, the phase relationship of the phasesof the slave ring oscillator 2004 relative to the phases of the masterring oscillator 2002. In this manner the widths of the pulses in the ndim control signals φ₁, φ₂, . . . , φ_(n) at the outputs of the S-PFD2006-1, 2006-2, . . . , 2006-n are changed in response to the modifiedpower supply, forcing the duty cycles of each of the n dim controlsignals φ₁, φ₂, . . . , φ_(n) to adapt to and track the duty cyclevariations of the A>B signal.

In the exemplary embodiments of the invention described above, the LEDs608-1, 608-2, . . . , 608-n of the LED bulb 600 are individually poweredby m separate power supplies provided by the divider 604. In analternative embodiment, the LEDs 608-1, 608-2, . . . , 608-n areconnected in parallel and powered by a single power supply, as in theLED bulb 2200 shown in FIG. 22. The AC-DC converter 602 operates similarto as described above, the parallel connection of the LEDs 608-1, 608-2,. . . , 608-n allowing for graceful degradation, similar to the LED bulb600. A DC-DC converter 2202 downconverts the DC output voltage Vdc1 to alower DC voltage Vdc2 for the LEDs 608-1, 608-2, . . . , 608-n.Alternatively, if the AC-DC converter 602 is not duty-cycle-limited atlow output voltages, it may possibly be configured to convert the ACinput voltage Vin directly to Vdc2, i.e., without requiring assistanceof the intermediate DC-DC converter 2202. The LED controller 2204includes circuitry for collectively or individually controlling thedimming of the LEDs 608-1, 608-2, . . . , 608-n, similar to the LEDcontroller 606 described above, including support circuitry forcontrolling dimming in response to conventional TRIAC dimmer switches.

While various embodiments of the present invention have been described,they have been presented by way of example and not limitation. It willbe apparent to persons skilled in the relevant art that various changesin form and detail may be made to the exemplary embodiments withoutdeparting from the true spirit and scope of the invention. Accordingly,the scope of the invention should not be limited by the specifics of theexemplary embodiments. Rather, the scope of the invention should bedetermined by the appended claims, including the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. A lighting system, comprising: one or morelight-emitting devices; and an alternating current to direct current(AC-DC) converter configured to convert an AC input voltage Vin to a DCoutput voltage Vout for powering said one or more light-emittingdevices, said AC-DC converter including a plurality of switches, acomparison circuit configured to determine times when Vin>Vout and timeswhen Vin<−Vout, and a switch control circuit configured to control saidplurality of switches based on comparisons performed by said comparisoncircuit.
 2. The lighting system of claim 1, wherein said AC-DC converteris configured to operate as a buck converter during times saidcomparison circuit determines that Vin>Vout and as an inverting buckconverter during times said comparison circuit determines thatVin<−Vout.
 3. The lighting system of claim 1, wherein said one or morelight-emitting devices comprises a plurality of independently-poweredlight-emitting devices and said lighting system further comprises apower divider circuit configured to generate a plurality of DC powersupplies from power provided by said AC-DC converter, said plurality ofDC power supplies used to supply power to said plurality ofindependently-powered light-emitting devices.
 4. The lighting system ofclaim 1, further comprising a dimmer circuit configured to generate alow-frequency signal having a duty cycle that is dependent upon themagnitude of an analog dim control signal provided by an external dimcontrol switch relative to said DC output voltage rout.
 5. The lightingsystem of claim 4, wherein said dimmer circuit is further configured toupconvert said low-frequency signal to a high-frequency digital dimcontrol signal for controlling dimming of said one or morelight-emitting devices, said high-frequency digital dim control signalhaving a duty cycle that is the same as the duty cycle of saidlow-frequency signal.
 6. A lighting system, comprising: one or morelight-emitting devices; and an alternating current to direct current(AC-DC) converter configured to convert AC power from an AC power sourceto DC power, said AC-DC converter including: a first plurality ofswitches configured to chop an AC input signal from said AC power sourceduring positive half cycles of the AC input signal, a second pluralityof switches configured to invert and chop said AC input signal duringnegative half cycles of the AC input signal, an inductor coupled to oneor more switches of said first and second pluralities of switches, andan output capacitor coupled to one or more switches of said first andsecond pluralities of switches.
 7. The lighting system of claim 6,further comprising a controller having a comparison circuit configuredto compare the magnitude of an AC voltage from said AC power source orscaled version thereof to a DC voltage produced by said AC-DC converter,compare the magnitude of said AC voltage or scaled version thereof tothe negative of said DC voltage, and produce switch control signalshaving duty cycles based on said comparisons.
 8. The lighting system ofclaim 7, wherein said controller further comprises dim control circuitryconfigured to control dimming of light emitted by said one or morelight-emitting devices depending on the comparisons performed by saidcomparison circuit.
 9. A lighting system, comprising: one or morelight-emitting devices; and an alternating current to direct current(AC-DC) converter configured to convert an AC input voltage from an ACpower source to a DC voltage, said AC-DC converter including: aninductor, a first plurality of switches configured to repeatedly coupleand decouple said inductor to and from said AC power source duringpositive half cycles of said AC input voltage, a second plurality ofswitches configured to invert said AC input voltage and repeatedlycouple and decouple said inductor to and from said AC power sourceduring negative half cycles of said AC input voltage, and an outputcapacitor coupled to one or more switches of said first and secondpluralities of switches.
 10. The lighting system of claim 9, furthercomprising a comparison circuit configured to compare the magnitude ofsaid AC input voltage or scaled version thereof to said DC voltage,compare the magnitude of said AC input voltage or scaled version thereofto the negative of said DC voltage, and produce switch control signalshaving duty cycles based on said comparisons.
 11. The lighting system ofclaim 10, further comprising dim control circuitry configured to controldimming of light emitted by said one or more light-emitting devicesdepending on the comparisons performed by said comparison circuit.
 12. Apower conversion and control system for an electrical load, comprising:an alternating current to direct current (AC-DC) converter configured toconvert AC power from an AC power source to DC power; comparisoncircuitry configured to compare the magnitude of an AC input voltagefrom said AC power source or scaled version thereof to the DC outputvoltage produced at the output of said AC-DC converter, compare themagnitude of said AC input voltage or scaled version thereof to thenegative of said DC output voltage, and produce an output signal havinga duty cycle based on the comparisons; and control circuitry configuredto control current passing through said electrical load according to theduty cycle of the output signal of said comparison circuitry.